Converters are used to change the voltage level of a power source and/or to transfer power between a Direct Current (DC) and an Alternating Current (AC) connection. Converters are seen in all manner of electronic devices, from low power devices (for example, a battery in a computer may supply a particular voltage, but circuits therein may individually require a different voltage) to High Voltage Direct Current (HVDC) networks. For example, in the developing field of power transmission, it may be desirable to interconnect networks at different voltages, and/or convert from AC to DC or vice versa.
Bipolar converters, which have two connections with opposite polarity, each at a high potential with respect to ground, are known. Some bipolar converters have an advantage over monopole configurations in that, in the event of some faults such as pole-to-ground faults, the other un-faulted pole can remain in service, using either a ground return path or a dedicated neutral conductor as a return path. In such examples, even with one pole is out of service due to a fault, 50% of the capability of a converter may still be available (and with overload capability this can even be higher).